Notably, cathepsins A, B, C, D, H, L, S, and Z are representative hydrolytic enzymes influenced by an acidic environment.[14] Our data from a systematic proteomic analysis of 20 cases of primary ESCC tumor tissues, matched normal tissues, and lymph node metastatic tissues revealed that the expression of cathepsins A, B, C, D, H, L, S, and Z were elevated in tumor tissues (Figure 1D; Figure S1D, Supporting Information). Here, CTSA is linked to neoplasm.